1. Field of the Invention
The present invention relates to a stepping motor control circuit and an analog electronic watch using the same.
2. Description of the Related Art
In the related art, a 2 pole PM (Permanent Magnet) type stepping motor is used for an analog electronic watch and the like. The stepping motor includes a stator provided with a rotor receiving hole and a position determining portion for determining a stop position of a rotor, the rotor provided in the rotor receiving hole, and a coil. Further, the stepping motor rotates the rotor by magnetic flux generated in the stator by an alternating signal supplied to the coil, and stops the rotor at a position corresponding to the position determining portion.
As a low consumption driving scheme for the 2 pole PM type stepping motor, a correction driving scheme of a stepping motor has been put to practical use, which uses a main driving pulse P1 with low energy in a normal time, and a correction driving pulse P2 with high energy for performing driving in load variation. The energy of the main driving pulse P1 is reduced/increased according to rotation/non-rotation of a rotor, so that the stepping motor is driven with lower energy as much as possible (for example, refer to JP-B-61-15385).
The correction driving scheme is performed as follows: (1) the main driving pulse P1 is output to one pole O1 of a coil, and an induced voltage generated in the coil is detected by rotor vibration immediately after the main driving pulse P1 is output thereto; (2) the case in which the induced voltage exceeds a reference threshold voltage arbitrarily set is regarded as rotation, the main driving pulse P1 maintaining the energy is output to the other pole O2 of the driving coil, and the output of the main driving pulse P1 is repeated by a certain number of times so long as the rotor is rotated. If the number of times of output thereof reaches the certain number of times (PCD), the main driving pulse P1 with lower energy is output to the other pole O2, and this process is repeated again; and (3) the case in which the induced voltage does not exceed the reference threshold voltage is regarded as non-rotation, the correction driving pulse P2 with high energy is immediately output to the same pole, so that the rotor is forcibly rotated. In the next driving, a main driving pulse P1 with energy higher than the main driving pulse P1, which causes the non-rotation of the rotor, is output to the other pole, and the steps (1) to (3) are repeated.
Further, in the invention according to WO2005/119377, when detecting the rotation of the stepping motor, in addition to the detection of the induced signal, after a means is provided to compare a detection time with a reference time and the stepping motor is rotated by the main driving pulse P11, the correction driving pulse P2 is output if a detection signal is less than a predetermined reference threshold voltage Vcomp, and a next main driving pulse P1 is changed (pulse up) to a main driving pulse P12 having energy higher than that of the main driving pulse P11 so that the stepping motor is driven by the main driving pulse P12. If the detection time when the stepping motor has been rotated by the main driving pulse P12 is earlier than the reference time, the main driving pulse P12 is changed (pulse down) to the main driving pulse P11, so that the stepping motor is rotated by the main driving pulse P1 according to a load during the driving thereof, resulting in reduction of current consumption.
However, when the stepping motor is used for an analog electronic watch, the rotation or non-rotation state occurs according to the driving pulse as described above. However, when force acting on the rotor is significantly changed as in the case of calendar feed or variation in supply voltage, a case may occur in which the rotor infrequently stays in an intermediate position different from a stationary position, so called a case may occur in which the rotor is in an intermediate stationary position, a problem may occur in which rotation or non-rotation is abnormally determined, or hand movement delay may occur.